In the operation of any internal combustion engines, and particularly engines of the diesel type, a hot, rapidly flowing exhaust gas stream is created. While the exhaust streams from both engines will carry a certain amount of particulate matter, the diesel normally carries a much greater amount than does the ordinary spark ignited engine.
In the instance of a diesel engine such particles represent a product of combustion which is passed from the engine combustion chamber, through the engine filter or muffler, and into the atmosphere. These particulate products of combustion normally comprise bits of carbon and are clearly identifiable in the operation of any diesel engine by the dark smoke which is sometimes emitted as exhaust gas.
The offensiveness of these carbon particles is emphasized under certain engine conditions when a particularly heavy smoke is ejected. Often such a period occurs during a sharp acceleration period of when the engine is idling.
A diesel engine exhaust gas temperature will vary in response to the load and speed at which the engine operates. Consequently, the degree to which combustible particulate matter will be burned, varies. It is expected therefore that under some engine conditions there will be a greater amount of the particulate products of combustion than at other conditions.
Since the ordinary diesel frequently operates at lower temperatures, it is desirable that the exhaust gas be treated such that particulate matter is removed from the exhaust stream. This is achieved in one respect by the imposition of a filter medium in the exhaust system.
The normal exhaust gas filter comprises a means for intercepting the gaseous flow and for retaining the combustible particles within the passages of the filter media. Such filters are well known in the art and are used in many instances where it is desired to retain particulate matter from being carried by a gaseous stream.
However, in the instance of an engine of the type contemplated, it is found that particles which are accumulated in the filter will eventually impair gas flow therethrough. The ultimate result could be the complete blocking of the filter bed such that the gas stream will no longer pass and consequently impede operation of the engine.
It has therefore been found necessary in the use of such smoke eliminating or particle-retaining filters, to periodically purge the filter bed such that the combustible matter will be incinerated and removed. Further, it is found practical to achieve this particle incineration step on a time basis to assure optimum filtering capability of the filter under all engine operating loads.
In one form of filter bed utilized in such a gas treating apparatus, the filter media comprises a mass of randomly disposed fibrils or metallic wires. The latter are disposed to form discrete gaseous passages therethrough. This type of filter media is found to be highly effective for removing particulate matter since the media has the effect of providing the greatest contact area between the passing gas stream and the filter surfaces.
This type of filter, however, is fragible and susceptible to damage and distortion due to excessive temperatures which might be reached during the incineration period. The thin fibrils will then be weakened and distort, thereby instituting openings which permit the hot exhaust gas to bypass the filter bed.
To promote the retention, and subsequent eventual incineration of combustible particles, the filter media can be provided with a catalytic material. Thus, incineration of the particles will occur at a lower temperature than if a catalyst is not utilized. A further advantage to the method of treating engine exhaust gases at regular intervals, is that the incinerating period need only be maintained for relatively short intervals to purge the filter bed or beds.
Toward overcoming the foregoing problems, the present filter is provided, into which a hot exhaust gas stream carrying solid combustible particles can be introduced. The filter comprises a series of rigid filter beds which are carried within a surrounding housing or casing and which are spaced one from the other by intermediate spacer members disposed therebetween.
Turbulation chambers which are defined between adjacent filter beds can be provided with a frangible filter medium such as steel wool or the like. However, the beds themselves are fabricated of a monolithic structured, disc-like member which is retained within the steel filter casing or housing. The latter is provided with access means whereby a flow of hot exhaust gas can be caused to flow through the serially aligned filter beds.
It is therefore an object of the invention to provide a filter of the type contemplated for efficiently and effectively treating a hot diesel exhaust gas stream. A further object is to provide a filter of the type which is capable of removing combustible particulate matter from a hot exhaust gas stream. A still further object is to provide a filter which is adapted to be rejuvenated periodically by incineration of retained combustible particles such that the filtering components are not adversely affected by excessive temperatures.